1. Field of the Invention
The present invention relates to single-channel and multi-channel detectors capable of recording low-level signals which may include as few as several electrons. Specifically, the invention is an amplifying avalanche device wherein amplification is realized via a multi-layered, solid-state intelligent amplifier design. Structures have immediately applicability to devices critical to homeland defense.
2. Background
The detection and recording of low-level signals is particularly challenging to sensor devices. For example, the sensitivity, selectivity, operational range, and arrayed arrangements of such devices require precision detection of signals comprising as few as several electrons.
One widespread approach for detecting and recording low-level signals includes charge-sensitive amplifiers on field-effect transistors having a threshold sensitivity of a few dozen electrons, as described by Albert J. P. Theuwissen in Solid-State Imaging with Charge-Coupled Device, published by Kluwer in 1995 (ISBN 0-7923-3456-6).
Another approach includes output video signal amplifiers in a charge coupled device ensuring nearly the same sensitivity as charge-sensitive amplifiers on field-effect transistors.
Yet another approach to sensing weak electrical signals is the use of avalanche amplification or multiplication of signal carriers, which generally is the most sensitive and high-speed method of amplification. Avalanche-type devices include those described by F. Capasso in Physics of Avalanche Photodiodes in Semiconductors and Semimetals, published by Academic Press in 1985 Vol. 22.
Avalanche amplification is based on impact ionization arising in a strong electric field, wherein the signal carriers accelerating in an electric field ionize the atoms of the working medium of the amplifier, thus resulting in multiplication (e.g., duplication) of the signal carriers. At a high multiplication factor, however, it is difficult to stabilize the avalanche amplification operating point. Additionally, the internal (excessive) noise level and response time grow rapidly with an increasing multiplication factor. As such, traditional avalanche photodiodes use a rather low multiplication factor, M, typically less than 103, which prevents the detection and recording of signals consisting of several electrons in a wide band.
Avalanche multiplication has also been applied to recording individual ionizing particles using a Geiger-Muller counter, as described by Ekstrom in U.S. Pat. No. 4,303,861. A particle entering such a device initiates an avalanche-like process of multiplication of the signal carriers up to a necessary recording level. More recently, this principle has been successfully used for recording single charge carriers in semiconductor avalanche-type photodiodes. This Geiger-Muller principle of amplification, however, does not allow for distinguishing between signals within one or several input charge carriers (i.e., it does not provide high resolution for a number of charge carriers).
Shushakov et al. in U.S. Pat. No. 6,885,827 describes and claims a system and method for the detection of an input signal by distributing the input signal into independent signal components which are independently amplified, thus uniquely enabling a high amplification factor, low noise, and rapid response speed. The invention includes several steps. A signal is allocated on individual channels of a multi-channel threshold amplifier in such a manner that each channel has only one elementary electric charge. Each channel of the amplifier converts the single electron at the input into a calibrated charge packet at the output. Summation of the output signals of each channel allows the measurement of the value of the few electron electric signals communicated to the input of a discrete amplifier with high accuracy. The calibrated amplification of a single electron at each channel of the discrete amplifier is provided. In addition to a threshold avalanche amplifier, each channel is equipped with an integrator to accumulate an amplified charge signal packet. After receiving a required charge packet, an integrator communicates with a quantifier through a governor, which turns the channel OFF. A governor is used to control the potential of the quantifier and to drain the charge from the integrator for the purpose of transferring the channel back to its initial state.
It may be appreciated, therefore, that there remains a need for further advancements and improvements thus enabling the detection of weak signals. Accordingly, what is required are amplifying avalanche structures, compatible with the system and method provided by Shushakov et al. in U.S. Pat. No. 6,885,827, capable of further advancing and improving the detection of weak signals.